Electric discharge device of the gas filled type



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BLEc'rnIc DISCHARGE DEVICE oF THE GAS FILLED TYPE 'Fnea'nprl 1?, 194s i?@l il PRESSURE TIMES DISMNCE Ihvevrwtov: Stahleg R. Fitimarris,

bg JM Hi: Attorneg.

Patented Oct. 7, 1947 ELECTRIC DISCHARGE DEVICE or 'rnE cas FILLED TYPEStanley R. Fitzmorris, Schenectady, N. Y., assignor to General ElectricCompany, a corpi)-v ration o! New York Application April 17, 1943,Serial No. 483,409

29 Claims. (Cl. Z50-27.5)

My invention relates to electric discharge devices, and moreparticularly to electric discharge devices of the controlled type whichemploy ionizable mediums such as gases or vapors.

It is an object of my invention to provide new and improved electricdischarge devices.

It is another object of my invention to provide new and improvedelectric dischargev devices of the controlled type wherein ionizablemediums,

such as gases or vapors, are employed.

It is a further object of my invention to provide new and improvedelectric discharge devices wherein the electrodes of the devices arespaced in close relationship, and wherein the pressure oi the ionizablemedium ls maintained at a relatively large value while maintaining alarge maximum forward voltage rating, a relatively large inverse orarc-back voltage, and stable operation.

It is a still further object of ymy invention to provide new andimproved electric discharge devices wherein the transfer of currentbetween the anode and the cathode is effected by an arc discharge orglow discharge phenomenon and wherein the immediate region within whichthe ionization takes place is limited to a relatively small proportionof the total volume of enclosed ionizable medium.

It is a still further object of my invention to provide new and improvedstructure for electric discharge devices of the type employing ionizablemediums wherein the spacing between the enclosed electrodes is verysmall and wherein the ionization region is confined by mechanical meansand by virtue of the establishment of a relatively small mean free pathof the ions constituting the medium.

Briefly stated, I provide new and improved electric discharge devices ofthe type employing an ionizable medium, such as a gas or a vapor. Moreparticularly, I provide discharge devices of the controlledarc-discharge type wherein a gas or vapor pressure of relatively largevalue is used while maintaining a large maximum peak forward voltagerating, a large inverse or arc-back voltage rating, and stability ofoperation.

The electric discharge devices which I provide` are characterized by theutilization of very small electrode spacings and the use of a gas orvapor pressure of relatively large value, thereby obtaining a smallvalue for the product of anodecathode spacing and the gas or vaporpressure whereby large forward and inverse voltage ratings are afforded.Forward voltage rating may be defined as the positive anode-cathodevoltage which a discharge device will withstand, Iwith proper gridvoltages applied, without effecting the establishment of an undesired oruncontrolled discharge between anode and cathode.v By inverse voltagerating is meant that instantaneous value of voltage that the discharge'device will safely' withstand in the direction opposite to that inwhich it is designed or intended to transmit current. l

For a better understanding of my invention, reference may be had to thefollowing description taken in connection with the accompanying drawing,and its scope will be pointed out in the appended claims. Fig. 1 of theaccompanying drawing diagrammatically illustrates my invention asapplied t'o a construction, certain features of which are disclosed andclaimed in copending patent application Serial No. 436,633 of James E.Boggs, filed March 2,8, 1942, and which is assigned to the assignee ofthe present application. Fig. 2 represents details of a cathodeconstruction which I employ. Fig. 3 represents generally therelationship existing between the sparking potential and the product ofpressure and distance between electrodesV within an ionizable medium,`which relationship is now somewhat generally known as Paschens Law. Fig.4 is a modiiied electric discharge device construction employing myinvention. i

Prior to a detailed consideration of the illustrated embodiments of myinvention, it is believed appropriate to review certain general aspectsthereof. Heretofore, the substantial utilization of the inhibiting eecton evaporation of the cathode material in electric discharge devicesoperating under relatively high pressure of an ionizable medium, such asa gas or a vapor, has not been attainable in high voltage devices, thatis devices having high forward and inverse voltage characteristics, byvirtue of the fact that structures of reproducible characteristics werenot available for maintaining relatively close space relationshipsbetween the anode and cathode of the discharge devices and forestablishing a single discharge path between anode and cathode. The useof vapor or gas pressures of relatively high value is desirable sincesuch pressures inhibit the evaporation of cathode material, that isinhibit the evaporation of the cathode emissive surfaces such asalkaline earth metals or oxides thereof. Furthermore, the use ofrelatively high pressures is desirable in order to reduce the amount ofgas clean-up. The term gas cleanup is somewhat generally used to denotethat phenomenon which occurs in discharge devices 3 y O 1 employingionizable mediums, particularly gases, whereby upon operation thebombardment of the cathode by the positive ions incident to the aredischarge causes absorption of the medium by the enclosed parts, thedislodged cathode material and internal surface of the enclosingenvelope. By the useof relatively high gas or vapor pressure, thisabsorption is substantially reduced, consequently resulting in increasedlife of the discharge devices.

While heretofore someof the prior ari;` discharge devices have employedrelativelyv high f pressures, these devices have been subjected to adefinite limitation of having relatively low forward and inverse voltageratings. By virtue lof the discharge device constructions and therelationships described hereinafter, I provide electric dischargedevices of the type employing ionizable mediums wherein the advantagesvof inhibiting cathode material evaporation and relatively large forwardand inverse voltage ratings are both attainable. In an electricdischarge emloying a plurality or pair of electrodes such as an anodeand cathode within an ionizable medium, there is a definite relationshipbetween the sparking or break-down'voltage and the product of thepressure of the medium and the distance between the electrodes. Thisrelationship is shown generally in Fig. 3 where the ordinates representthe breakdown voltage and abscissae represent the product of pressureand distance. Of course, for each gas or vapor, or combinations thereof,a distinctive individual curve will be representative of thisrelationship. The characteristics depend, among other factors, on theconfiguration of the electrodes, the materials or metals of which theelectrodes are constituted and the nature of the electrode surfaces.Furthermore, there is a definite minimum or critical sparking orbreak-down potential as illustrated by the general characteristic Jshown in Fig. 3.

By the use of the term sparking potential or break-down potential ismeant that phenomenon in which a discharge is established in the absenceof local ionization or arc producing means. For example, this phenomenonis somewhat generally referred to as a Townsend discharge and is not ofthe self-sustaining type requiring the application of an external sourceof energy to maintain it. This type of phenomenon, of course, usuallyprecedes and is distinguishable from a glow discharge or an arcdischarge wherein the potential differences across given electrodes aresubstantially less than in the sparking region due to the fact thatappreciable ionization of the medium occurs, effecting a reduction 'inthe voltage appearing across the electrodes.

In accordance with one aspect of my invention, I provide electricdischarge devices wherein the structural spacing is correlated withrespect to the operating pressure of the medium, such as a gas, toobtain a relatively small product of pressure and distance, therebygiving to the discharge device a large break-down voltagecharacteristic, except for the controlled arc discharge in the desireddirection of conduction. Furthermore, by virtue of the fact that themedium or gas pressure is maintained at a relatively high value duringoperating conditions, the mean free path of the ions constituting thegas may be maintained at a relatively small value with respect to theanode-cathode spacing, preferably Within the neighborhood of one-sixthof the anode-cathode spacing, resulting in a substantial transverse orradial localization of the region Within which the .4 i arc dischargephenomena between the anode and cathode occur. Due to the fact that thegas pressure is relatively large, the mean free path of the ions issmall with respect to the anode-cathode spacing, resulting in aconfinement of the arc discharge path, which may be considered from anelementary point of view as arising from the recombination .of thel ionsas they tend to depart from the localized arc discharge region. It willbe appreciated that as the ions tend to move from the localized region,upon moving into the relatively highpressure region of the non-ionizedgas, the ions re-combine with the relatively inactive gas surroundingthe ionized region.

The immediately above described feature may be considered as augmenting,to a certain extent, a gas focusing phenomena established primarily bythe fringing effect of the electrostatic field extending from edge orperiphery of the cathode surface to the anode surface. g

In order to accentuate the above described phenomena whereby theionization of the medium is localized, I provide electric dischargedevice constructions wherein the amount of gas actively or immediatelyengaged inthe arc discharge or glow discharge and which is mostsusceptible to clean-up is localized within a particular part,

or parts, of the discharge device enclosure without limiting the totalvolume of gas or medium available, thereby lending to the device thedesired long life. The anode and cathode cooperating surfaces, asillustrated in the embodiments of my invention described hereinafter,are preferably located within a confined part of the structure, andadditional means such as mechanical means is provided for limiting theeffective longitudinal cathode area over which theglow-dischargephenomena may occur. Furthermore, the discharge deviceconstructions, and particularly the enclosed envelope constructions, arearranged -so that the total enclosed volume of the ionizable medium orgas is substantially greater than the volume of the region within whichthe immediate are discharge phenomena and glow discharge phenomena takeplace. For example, I have found that the desired arc discharge and theglow discharge phenomena may be effectively localized withoutsacrificing the desired life of the discharge devices by employingconstructions wherein the total enclosed volume of the medium or gas isat least ve or ten times the volume of the region within which the abovephenomena occur. Of course, it is to be appreciated thatthis ratio isnot critical and that an important aspect is the provision of asufficiently large reservoir of medium or gas within the enclosingenvelope to afford the desired replenishment of the gases absorbed bythe clean-up process during operation.

Referringl now particularly to Fig. 1', one embodiment of my inventionAis there illustrated which comprises a plurality of planar electrodes,such as an anode, a cathode and a grid, enclosed within an envelope andvin which an ionizable medium such as a gas is employed. 'I'he dischargedevice comprises a plurality of transversely extending metallic membersI, 2 and 3 which constitute parts of the enclosing envelope and also mayserve to support the cooperating electrodes of the discharge device.Members i and 2 may be of substantially disk formation provided withapertures 4 and 5, respectively, and transverse member 3 may comprise apart of a cylindrical member 6 of which member 3 comprises an inwardlyextending ange. The cylindrical member E is preferably sealed to a baseamaca:

member 'l which is provided with a plurality of' 4 terminal prongs B-II, inclusive, and an orienta-1 tion protuberance I2 which are arrangedfor insertion into an appropriatesocket. Transverse -members I, 2 and 3a're maintained in illustratedv or a plurality of lead-in or rigidsupporting conductors III and 3l which are connected to terminal prongs!and II, respectively.

` I also contemplate in a discharge device of the Yabove describednature the provision of suitable getteringl means which may` comprise. aribbon 32 ofgettering material which is supported by a pair of lead-inrods or .conductors 32 and 34 smaller longitudinal dimension than thecylinder v I4 for the purpose of dening a' relatively small region'between transverse members I and 2 for purposes which will be explainedin detail here-y inaiter.

An anode I5, preferably comprising a solid disk of metal such as nickelor molybdenum, is provided with an appropriately formed shoulder. toengage transverse member I to which it is welded or soldered, and isprovided with a planar anode` surface I8. In close proximity to theanode surface I8 and supported on the upper surface vvoit which areconnected to suitable terminal prongs (not illustrated). The getteringoperation is effected by the transmission of electric current throughthe ribbon 32 to effect substantial vaporl ization of the materialincluded thereon or therein transverse member 2, I provide a gridl I1preferf ably of the mesh type and which may be deformed upwardly to havethe configuration illustrated.

Transverse member 2 also serves the purpc'isel of affording anexternally accessible connection.

to the grid Il, and connection to the anode of the discharge device maybe obtained eitherv through a direct connection to the disk I5 or toAthe transverse member I which is in electrical contact therewith.

I employ a cathode construction, which permits l the provision ofclosely positioned anode and cathode cooperating surfaces, and whichextends through aperture 5 in transverse member 2. The cathodeconstruction may comprise a metallic cathode cylinder I8, shown indetail in Fig. 2,

having a closed end I9 which constitutes the cathode emissive surface.This surface preferably lies in a plane above the upper surface ofmember 2 and may be coated with an electron emissive material such as analkali or alkaline earth metal, or oxides thereof. Suitable operatingtemperatures for the cathode structure may be obtained by the provisionof a fllamentary cathode heating element 20 which is positioned withinthe cathode structure, and more particularly within a cylinder 2i, whichtelescopes and is conl centric with cathode cylindery I8, being providedwith a metallic end disk 22 seated upon the inner surface of the endpart I9 of cylinder I8 to adord the desired thermal connection with theclosed end of cylinder I8.

'Ihe above described cathode construction may be supported by a ilangedtubular member 23, illustrated in Fig. 2, and which comprises a angepart 24 and an integral tubular part 25 provided with a dared section 26upon which the lower end of the cathode cylinder I8 rests, therebyproviding a structure readily adaptable for .manu.

facturing operations andfor obtaining a desired localization of the heatincident to the element 20. The above described cathode heatingstructure may be supported directly by transverse member 3 or cylinder 6or may be supported by and insulated therefrom by means of an annularinsulator 21. Alternatively, the cathode structure may be supported byrigid cathode conductors to be described presently.

The circuit for energizing the cathode heating element 20 may comprise apair of lead-in conductors 28 and 29 which are connected to terminalprongs 9 and I0, respectively, and connection to the cathode may beobtained by a single which cooperatesl with undesirable gases within theenvelope andl which it is desired to absorb either during the evacuationprocess or immediately thereafter.

As a means for further localizing the glow discharge phenomena, that isfor limiting the eiective area of the cathode cylinder I8 which maybeinvolved in the glow discharge phenomena, I provide means, such as adielectric disk 35.

which surrounds the cathode cylinder I8 and whiclris of greaterdimension than the aperture .5 in ltransverse member 2. Disk 35 may beconstructed ofa suitable material, such as mica, and may be displaced asmall distance from the under ysurface of transverse member 2. Disk 35may be supported by any suitable construction and is illustrated asbeing supported by a metallic cylinder 36 which is welded or soldered tothe upper surface of ilange 24 of the cathode supporting structure.

In electric discharge devices which I have built and tested, I havefound that anode-grid spacings preferably lie'within the range of 10 tol5 mils and the grid-cathode spacing is preferably Within a range of 2to 10 mils. In the latter case, the distance between the cathode andthegrid is that measured from the closed end of the cathode cylinder I8.Considering the range of pressures, it may be generally stated that Iprefer to utilize a sufciently high pressure of the gas or` vapor toobtain a product of pressure and distance equal to or less than one-halfthe product which corresponds to the minimum sparking potential for theparticular medium. More speciiically, I prefer to employ a sufficientlylarge pressure to obtain long life in conjunction with the maximuminter-electrode spacing, particularly between the remotest sections ofanode and grid, or anode and cathode and supporting structures therefor,to obtain a product of pressure and distance which establishes largespark breakdown or arc-over voltage characteristics.

In obtaining the large forward and inverse voltage ratings by operatingat a relatively small product of pressure and inter-electrode spacing,itis important to maintain the distances between the electrodesupporting structure as well as the cooperating surfaces of theelectrodes at relatively small values where the desired range of highpressures is employed. Stated in other words, the maximum distancebetween the elecis small for the pressure employed. Furthermore, sincetransverse member 2 is intermediate disk 35 and the anode l5, the meetsthis criterion.

' The mesh-type grid l1 may completely cover aperture 5 and beconstructed of a wire or a. plurality of wires of relatively smalldimension, such as a diameter of 2 mils, providing a large number ofrelatively small openings. For example, one type of mesh grid which Ihave found to serve satisfactorily is .a mesh grid comprising aplurality of 2.mi1 wires defining one hundred openings per linear inch,that is, providing a plurality of 8 mil square openings.

The ionizable medium employed within discharge devices of the abovedescribed character may be an ionizable vapor or an inert gas such asargon, neon, xenon, or helium, preferably having an operating pressurelying Within or above the range of 1.5 to 2.0 millimeters of mercury.

Curve A of Fig. 3 represents the relationship existing between thebreak-down voltage and the product of pressure times distance for a pairof electrodes placed within an ionizable medium, such as a gas. Wherethe pressure is expressed in millimeters of mercury and the distance incentimeters, the minimum or critical ionizing potential appearing atpoint b for argon is approximately 0.9. As stated above, in dischargedevices built in accordance with my invention, the pressure iscorrelated with respect to the relatively short structural spacing toobtain a break-down or sparking potential lying preferably within theneighborhood of 0.2 such as that indicated at point c.

Considering one particular example, in a discharge device constructed inaccordance with my grid-anode structure invention, argon was employed asthe ionizable medium at an operating pressure of 1.6 millimeters. Thearc drop, that'is the voltage drop across anode and cathode, wassubstantially 13 volts at 50 milliamperes of anode-cathode current,providing a high voltage rating, having been successfully operatedwithin the neighborhood of 1000 volts. f

In other types of discharge `devices built in accordance with myinvention, I have found that high forward and inverse voltage ratingsare obtained by employing anode-cathode spacing of substantially 20 milsand using a gas, such as argon, having an operating pressure rangingfrom 1.8 to 2.0 millimeters of mercury.

Of course, the grid control characteristics of discharge devices of thetype shown in Fig. 1 indicate the necessity of employing an increasinglynegative voltage on the grid as the anode-cathode voltage is increased.In this connection, for the application of a given negative voltage tothe grid, an increase in plate voltage above a predetermined value orrange of values will initiate an arc 0r glow discharge. Conversely, ifit is desired to maintain the discharge device nonconducting, upon theapplication of increased anode voltage the grid potential must becorrespondingly increased in accordance with the grid-controlcharacteristic to prohibit the establishment of an arc discharge.

Another modification of my invention is illustrated in Fig. 4 which issimilar in many respects to that shown in Fig. 1, and correspondingelements have been assigned like reference numerals. In the arrangementof Fig. 4, a, shell or hood-type cylindrical grid connection member 31is provided which comprises an integrally formed shoulder or collar 38which surrounds transverse Vthe elect-ric discharge device.

. member 31.

8 member 2 and is electrically connected thereto. If desired, anadditional annular metallic spacer 39 may be placedintermediatetransverse member 2 and collar 38 to act as a rigid support therefor andwhich may be welded or soldered thereto. The anode structure comprises ametallic cylinder 40 having a closed end 4|, the surface thereof facingthe cathode constituting the anode for Cylinder 40 is supported by andsealed to an annular vitreous part 42 which is also sealed to the innersurface of The above described constructions for electric dischargedevices offer definite advantages. One of these advantages is theestablishment of a single confined or isolated path along which the arcdischarge phenomenon occurs. It will be noted that by virtueof the closespaced relationship between the end I9 of cathode cylinder I8, theregion through which an arc discharge may take place is isolated fromthe surrounding structure. Another advantage incident to the abovedescribed structure is that thegrid l1 shields the structure therebelowincluding the cathode, portions of transverse member 2 and themechanical arc or glow discharge confining means, thereby protectingthese elements or parts during the application of inverse voltage to theanode and cathode and consequently serving to relieve the electrostaticstress thereon incident to the applied voltage.

A further advantage incident to the above described structure is theresultant reduction in arc drop during normal operation of the dischargedevice incident to the relatively high gas pressure. I have found thatin discharge devices employing argon this .decrease in arc voltageranges from 2 to 3 volts.

A still further advantage resides in the fact that the structure affordsrelatively large surfaces exposed to the medium which has undergoneionization as compared with the volume within which the ionization takesplace. Thisaspect is of considerable importance in controlling thedeionization time of a discharge device of this character. For example,it will be noted that the inner surface of the enclosing envelope, theface or anode surface and the inner surfaces of transverse member '2immediately surrounding the aperture 5 are relatively large comparedwith the volume above the upper surface of disk 35, thereby providing arelatively large effective area for the neutralization or collection ofions after the intended period of conduction by the discharge device. Ofcourse, due to the increased operating pressure of devices of thischaracter, there is present in a unit volume of medium or gas a largernumber of ions than would be present with smaller operating pressuresand the diffusion rate is correspondingly slower. This, of course, initself would result in an increased deionization time. However, theadvantage obtained by the increased eiTective area compensates for theincrease in deionization time due to the increased pressure.

Although the yembodiments of my, invention illustrated are shown asincluding a control element or electrostatic grid placed between theanode and the cathode, it will be appreciated that the broader aspectsof my invention, whereshield grid.

While my invention has been illustrated as applied to a particular typeo f electric discharge devices employing elements or electrodes havingparticular configurations, it will be obvious to those skilled in theart that changes and modifications may be made without departing from myinvention, and I, therefore, aim in the appended claims to cover allsuch changes and modifications as fall within the true spirit and scopeof my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric discharge device employing an ionizable medium andincluding a plurality of electrodes comprising an anode and a. cathodehaving extended surfaces in opposed closely spaced relation, an envelopestructure enclosing said electrodes comprising means supporting saidelectrodes including a pair of transverse metallic members in spacedrelation and means comprising an insulating member sealed between saidmembers, and a member surrounding said cathode and extending outwardlytherefrom adjacent the extending surface of the cathode, said memberextending in closely spaced relation with respect to one of saidtransverse members, said member, said one transverse member, said anodeand said cathode providing a, chamber of relatively small volumeenclosing the extended surfaces of said anode and cathode and openinginto the interior of said envelope through the space between said memberand said one of said transverse members.

2. An electric discharge device employing an ionizable medium andincluding a, plurality of electrodes comprising an anode and a cathodein close spaced relation, and an envelope structure enclosing saidelectrodes comprising means supporting said electrodes including a pairof transversely extending members and means including a sealedinsulating member between the transverse members, the product ofoperating pressure of said medium and the spacing between said anode andsaid cathode being substantially less than the value of such productcorresponding to the minimum break-down voltage between the electrodesto obtain a large forward voltage characteristic and means including aportion of said envelope dening a localized region around said anode andcathode surfaces in which the discharge takes place, the volume of saidenvelope being several times the volume of said localized region toprovide a reservoir of said medium substantially in excess of thatemployed in the immediate arc discharge phenomenon between said anodeand said cathode.

3. An electric discharge device employing an ionizable medium andincluding a plurality of electrodes comprising an anode and a. cathodein close spaced relation, and an envelope structure enclosing saidelectrodes comprising means supporting said electrodes including a, pairof transversely extending members and means including a sealed tubularinsulator extending therebetween, the operating pressure of said mediumand the spacing between said anode and said cathode providing only alimited region of ionization of said medium and the enclosed volumedened by said envelope structure being at least ve times as great assaid region within which the immediate arc discharge phenomenon takesplace.

4. An electric discharge device comprising an l0 inert gas as anionizable medium and including a plurality oi! electrodescomprising ananode, a grid, and a cathode, said anode and grid being mounted in closespaced relation, and an envelope structure enclosing said electrodescomprising means supporting said electrodes including a pair oftransversely extending metallic members and means comprising a sealedinsulating cylinder between said members, the operating pressure of saidgas'being in excess of a pressure of 1.5 millimeters of mercury andtheproduct of said gas pressure and the spacing between said anode and gridbeing substantially less than the value of such product for minimumbreakdown voltage between the electrodes thereby to obtain large forwardand g inverse voltage ratings.v

5. An electric discharge device comprising an ionizable medium andincluding a plurality of electrodes comprising an anode and a cathode inclose spaced relation, and an envelope structure enclosing saidelectrodes comprising means supporting said electrodes including a. pairof transversely extending members and means comprising a sealedinsulating cylinder between said members, said cathode being ofcylindrical conguration supported by one of said members and extendingwithin said cylinder towards said anode providing an electron emissivevsurface for cooperation therewith, the operating pressure of saidmedium being in excess of a pressure of 1.5 millimeters of mercury andthe product of said operating pressure and maximum spacing betweencooperating surfaces of said electrodes and the supporting structuretherefor being substantially less than the value of such productcorresponding to minimum breakdown voltage between the electrodes.

6. An electric discharge device comprising an ionizable medium andincluding a plurality of electrodes comprising an anode, a grid and acathode in close spaced relation, and an envelope structure enclosingsaid electrodes comprising means supporting said electrodes includingthree transversely extending metallic members for said envelopestructure comprising an insulating cylinder sealed between thetransverse members supporting said cathode and said grid and a secondinsulating cylinder of substantially smaller longitudinal dimension thanthe first mentioned cylinder and sealed between the transverse memberssupporting said grid and said anode, said cathode being of cylindricalconguration and extending through an aperture provided by the transversemember supporting said grid, the product of the operating pressure ofsaid medium and the maximum spacing between said anode, grid, and saidcathode being substantially less than the value of such productcorresponding to minimum break-down voltage between said electrodes.

7. An electric discharge device comprising an ionizable medium andincluding a plurality of electrodes comprising an anode, a grid and acathode in close spaced relation, an envelope structure enclosing saidelectrodes comprising means supporting said electrodes including threetransversely extending metallic members and an insulating cylindersealed between the transverse members associated with said cathode andsaid grid and a second insulating cylinder of substantially smallerlongitudinal dimension than the first mentioned cylinder and sealedbetween the transverse members supporting said grid and-said anode, saidcathode being of cylindrical conilgllration and extending through anaperture provided by the transverse member supporting said grid,

anode, a grid and a cathode, said anode and said grid being in closespaced relation, an envelope structure enclosing said electrodescomprising means supporting said electrodes including a series oftransversely extending metallic -members and a plurality of insulatingcylinders respectively sealed between the various members, and means forconning the ionization region between said anode and said cathodeincluding means extending transversely of the envelope near the planarsurface of the cathode and cooperating with the transverse membersupporting one of said electrodes. y

9. An'electric discharge device comprising an ionizable medium andincluding a plurality of electrodes comprising a planar anode, a gridand a cathode, said anode and said grid being mounted in close spacedrelation, an envelope structure enclosing said electrodes comprisingmeans supporting said electrodes including a series of transverselyextending metallic members and a plurality of insulating cylindersrespectively sealed between the various members, and a transverselyextending member supported by the cathode structure and longitudinallydisplaced from the surface thereof parallel to said anode for limitingthe'ionization region. l

10. An electric discharge device comprising an ionizable medium andincluding a plurality of electrodes comprising a planar anode, a, gridand a cathode, said anode and said grid being mounted in close spacedrelation, an envelope structure enclosing said electrodes comprisingmeans supporting said electrodes including a series of transverselyextending metallic members and a plurality of insulating cylindersrespectivelysealed between the various members, the operating pressureof said medium being in excess of 1.5 milli` meters of mercury theproduct of said operating pressure and the maximum distance between saidanode and said cathode and supporting structure therefor beingsubstantially less than the value of such product for minimum break-downvoltage between said electrodes.

11. In an electric discharge device of the type employing an ionizablemedium and including a plurality of electrodes, the combinationcomprising an enclosing envelope comprising in part three transverselyextending members, a llair of insulating cylinders sealed in end-to-endrelationship between said members and constituting partof an envelopeenclosing said electrodes, said elec` trodes comprising an anodesupported by one end transverse member, a mesh electrostatic controlmember of the grid type supported by the intermediate transverse memberand a cylindrical cathode supported by the other end transverse memberand having an electron emissive surface i lying substantially in theplane of said intermediate member and extending into anv apertureprovided thereby, and means for establishing a coni-'med ionizationregion comprising a transverse member supported by the cathodestructure.

12. An electric discharge device employing an ionizable medium andincluding aplurality of electrodes comprising an anode and a cathode inclose spaced relation, and an envelope structure `enclosing saidelectrodes comprising means supporting said electrodes including a pairof tra-nselectrodes comprising an anode and a cathode in close spacedrelation, and an envelope structure enclosing said electrodes comprisingmeans supporting said electrodes including a, pair of transverselyextending metallic members and means for supporting said memberscomprising anv insulating member extending longitudinally therebetween,the product of the operating pressure of said medium in millimeters ofmercury 'and the maximum interelectrode spacing in centimeters beingsubstantially 0.2.

14. An electric discharge device employing an inert gas as an ionizablemedium and including a plurality of electrodes comprising a planar anodeand a planar cathode separated by a distance ranging from 18 to 20 mils,and an envelope structure enclosing said electrodes comprising meanssupporting said electrodes including a pair of transversely extendingmetallic members and means comprising a sealed insulating memberextending therebetween, the product of the operating pressure of saidgas in millimeters of mercury and the maximum spacing between said anodeand said cathode and supporting structures therefor in centimeters beingsubstantially less than that value corresponding to the minimumbreak-down voltage between said electrodes.

15. An electric discharge device employing argon as an ionizable medium.and including a pair of electrodes comprising an anode and a cathodespaced substantially 20 mils apart, and an envelope structure enclosingsaid electrodes comprising means supporting said electrodes including apair of transversely extending members and means comprising a sealedinsulating member extending therebetween, the operating pressure of saidargon gas being substantially 1.8 millimeters of mercury.

16. An electric discharge device employing an inert gas as an ionizablemedium and including a plurality of electrodes comprising an anode, agrid and a cathode, the cathode-grid spacing being substantially 6 milsand the grid-anode spacing being substantially 12 mils, and an envelopestructure enclosing said electrodes comprising means maintaining saidelectrodes in spaced relation including three transversely extendingmetallic members, said envelope structure comprising an insulatingmember sealed between the transverse members associated with saidcathode and said grid and a second insulating member of substantiallysmaller longitudinal dimension than Athe first insulating cylinder andsealed between the transverse members supporting said grid and saidanode, the product of the operating pressure of said inert gas and themaximum spacing between 13 a plurality of electrodes comprising ananode, a grid and a. cathode, the cathode-grid spacing beingsubstantially 6 mils and the grid-anode spacing being substantially 12mils, and an envelope structure enclosing said electrodes comprisingmeans supporting said electrodes including three transversely extendingmetallic members and an insulating member sealed between the transversemembers associated with said cathode and said grid and a secondinsulating member of substantially smaller longitudinal dimension thanthe ilrst insulating member and sealed between the transverse memberssupporting said grid and said anode, the operating pressure of saidinert gas lying within the range of 1.6 to 2.0 millimeters of mercury.

18. An electric discharge device employing an ionizable medium andincluding a plurality of electrodes comprising an anode and a, cathodein close spaced relation, and an envelope structure enclosing saidelectrodescomprising means supporting said electrodes including a pairof transversely extending metallic members and means forsupporting saidmembers comprising an insulating means extending therebetween, theoperating pressure of said medium being such that the mean free path ofthe ions constituting said medium is substantially one-sixth of thespacing between surfaces of said anode and said cathode.

19. An electric discharge device employing an ionizable medium andincluding a plurality of electrodes comprising an anode, a grid and acathode in close spaced relation, and an envelope structure enclosingsaid electrodes comprising means supporting said electrodes includingthree transversely extending metallic members and a pair of insulatingmembers sealed in end to end relation between the transverse members,the operating pressure of said medium being such that the mean free pathof the ions constituting said medium is not greater than one-fourth ofthe spacing between cooperating surfaces of said anode and said cathode.

20. An electric discharge device employing an ionizable medium andincluding a plurality of electrodes comprising an anode and a cathode inclose spaced relation, and an envelope structure enclosing saidelectrodes comprising means supporting said electrodes including a pairof transversely extending metallic members and means for supporting saidmembers comprising an insulating member extending therebetween, thetotal enclosed volume defined by said member being at least ten times asgreat as the volume of the region defined between planar cooperatingsurfaces of said anode and said cathode and the operating pressure ofsaid medium and the spacing between cooperating surfaces of said anodeand said cathode being correlated with respect to the pressure timesdistance sparking characteristic t'o produce a mean free path of theions constituting said medium having a value substantially one-sixth theinterelectrode spacing thereby eiecting a concentration of theionization phenomena within said region.

21. An electric discharge device employing an inert gas as an ionizablemedium and including a plurality of electrodes comprising an anode, agrid and a cathode. the cathode-grid spacing being substantially 6 milsand the grid-anode spacing being substantially 12 mils, and an envelopestructure enclosing said electrodes comprising means supporting saidelectrodes including three transversely extending metallic members andcomprising a pair of insulating members sealed in 14 end-to-end relationbetween said members, said grid being o! the mesh type comprising aplurality of 2 mil wires deilning substantiallyone hundred openings perlinear inch and being supported bythe transverse member intermediatesaid insulating members.

22. An electric discharge device employing argon as an ionizable mediumand including a. plurality of electrodes comprising an anode, a grid anda cathode, the cathode-grid spacing being substantially 6 mils and thegrid-anode spacing being substantially 12 mils, and an envelopestructure enclosing said electrodes comprising means supporting saidelectrodes in longitudinal spaced relation including three transverselyextending metallic members and comprising a pair of insulating cylinderssealed in end-to-end relation between 'said transverse members, saidgrid being of the mesh type and the operating pressure of said argonbeing correlated with respect to the anode-cathode spacing to produce anion mean free path substantially one-sixth the spacing betweencooperating surfaces of said anode and said cathode, and a, vtransversedielectric member surrounding said cathode and displaced from theintermediate transverse member towards the cathode base for limiting thedistance the glow discharge extends along the cathode toward its base.

23. An electric discharge device of the type employing an ionizablemedium and comprising a plurality of electrodes including an anode and acathode in close spaced relationship, an enclosing envelope structuresaid electrodes including three longitudinally spaced transversemetallic members and a vitreous cylinder sealed between one endtransverse member and the intermediate member and a second vitreouscylinder sealed between said intermediate member and the other endtransverse member, said intermediate member being provided with acentrally positioned aperture through which said cathode extends inproximity to said anode, and a transverse dielectric member surroundingsaid cathode and having a dimension greater than said aperture toprovide a localized region within which the glow and arc-dischargephenomena are confined.

24. An electric discharge device of the type employing an ionizablemedium and including a plurality of electrodes, and an envelopestructure enclosing said electrodes comprising three transverselyextending metallic members supported in spaced relation by a pair ofvitreous insulators sealed in end-to-end relationship with saidtransverse members, a thermionic cathode of cylindrical form supportedby one of the end trans- `verse members and extending to the vicinity ofan anode supported by the other end member through an aperture in theintermediate transverse member, a grid supported by said intermediatemember and in spaced relation between said anode and said cathode, andmeans for establishing a localized region within which the glow andarc-discharge phenomena occur comprising a transverse dielectric memberspaced below said transverse member and having a dimension substantlallygreater than the dimension of said aperture.

25. In an electric discharge device employing an ionizable medium, thecombination comprising a plurality of electrodes including an anode, acathode and a grid, an envelope enclosing said electrodes includinginpart a transverse disk provided with an aperture through which thecathode extends, agrid supported by said disk over said 15 aperture andspaced intermediate said cathode and said anode thereby shielding saidcathode during application of voltage across said anode and said cathodeand means cooperating with said disk to conne the arc dischargephenomenon to the region between saiddisk and said anode.

26. In an electric discharge device of the type employing an ionizablemedium, the combination comprising a plurality of electrodes includingan anode, a cathode land a grid, and an envelope enclosing saidelectrode and comprising in part a transverse metallic disk providedwith an aperture through which said cathode extends, said grid being ofthe mesh type attached to the surface of said disk facing said anode andcurved towards said anode to obtain relatively small spacingtherebetween.

27. In an electric discharge device of the type employing an ionizablemedium.' the combination comprising a plurality of electrodes includinga disk metallic anode, a cylindrical cathode and a mesh-type grid, andan envelope enclosing said electrode comprising in part a. transversedisk sealed to insulated supporting structure and being provided with acentrally located aperture through which one -end of said cathodeextends towards said anode, said grid being attached to the surface ofsaid transverse disk facing said anode and curved to lie in spacedrelation between an emissive surfaceA oi the cathode cylinder and theface of the disk anode.

28. In an electric discharge device of the type employing an ionizablemedium, the combination including a, plurality of electrodes including adisk-type anode and a cathode, an envelope enclosing said electrodesincluding a transverse metallic disk provided with an aperture throughlwhich said cathode extends thereby deilning with anode and said cathodeopening `into saidanode a localized region within which thearc-discharge phenomenon occurs, and a. partition member extending fromsaid cathode in closely spaced relation to said transverse disk andproviding with said transverse disk, said anode and said cathode aconfined region between said the interior of the remainder of saidenvelope through the space between transverse member and said partitionmember.

29. In an electric discharge device of the type employing an ionizablemedium at a pressure equal to or greater than 1.5 millimeters ofmercury, the combination comprising a plurality of electrodes includingan anodek and a cathode, and an envelope structure enclosing saidelectrodes comprising means defining a localized region within which thearc discharge and the glow discharge phenomena occur, the total volumeenclosed by said envelope being at least ve times the volume of saidlocalized region.

STANLEY R. FITZMORRIS.

REFERENCES CITED The following references are of record in the;

` le of this patent:

UNITED STATES PATENTS Smith Nov. 15, 1938

